"It’s a very, very tiny bone which is still protected in skull specimens. "It's the most successful place to extract DNA from," says Norman. Called the bony labyrinth, it lies within the inner ear and is one of the densest parts of the human body. "It’s quite common to find that the majority of the DNA is actually from the soil or bacteria which have invaded the skeleton after the person died," says Swedish geneticist Pontus Skoglund, who leads the ancient genomics laboratory at London’s Francis Crick Institute.Įxperts have discovered, however, one piece of the skeleton where intact human DNA can still be reliably found. Sequencing DNA from the skeletons of ancient plague victims found in mass burial sites is notoriously challenging, with scientists often having to work with the tiniest fragments of DNA, many of which are highly contaminated. "It was persistent and damaging, and anybody with the slightest advantage in that situation through their genetics would have been more likely to survive."īut until relatively recently, gathering any kind of data to answer this question was next to impossible. "The Black Death put a huge pressure on the human population in Europe," says Norman. The idea was that some of the individuals who survived it were able to pass on any genetic quirks that helped them do so to future generations. In particular, one theory suggests that the Black Death could have been widespread enough in the 14th Century to have created a form of natural selection. Over the centuries, however, plague is estimated to have killed at least 200 million people.īecause plague outbreaks were so catastrophic, researchers have long wondered whether they left some permanent imprint on the human immune system. More recent research on agricultural activity at the time – which would have plummeted amid so many deaths – has suggested that the toll may not have been so dramatic everywhere, with some regions being devastated by the disease and others barely touched. The Black Death is thought to have killed about 50 million Europeans by the mid 1300s, according to estimates based on historical records and accounts. It is thought to have originated in villages around the Chui Valley what is now Kyrgyzstan, perhaps passing through fleas from infected marmots into people before then spreading to Europe along the Silk Road trade route. But in the early 1300s, a strain of the bacteria exploded into Europe as the Black Death. DNA evidence of the bacteria has been found in skeletons dating back 4,000 years. Yersinia pestis is thought to have plagued the human species for thousands of years. In some parts of the world, such as Madagascar, the disease is more common.īut even though it is relatively rare compared to the past, the bubonic plague has left its mark on the human species and can still be found in the genomes of people living today. On average, around seven cases of plague in humans are reported in the US each year, although deaths are far less common with just 14 between 2000-2020. It still circulates in wild animals such as squirrels and prairie dogs, he adds. "There still are little pockets of plague in the US," he says. It is not something that comes as an enormous surprise to evolutionary geneticist Paul Norman, who studies bubonic plague at the University of Colorado, Anschutz. Most recently, a man in Oregon in the US, caught the bubonic plague from his pet cat. Even when it does occur, it can be relatively easily treated with antibiotics, saving lives. The disease is now vanishingly rare in both the US and Europe, largely thanks to changes in lifestyles that prevent it from spreading to humans from infected fleas as easily. The very mention of the words bubonic plague tends to provoke both fear and fascination even today. But it is responsible for a disease that once wiped out a third of Europe's population and caused millions of deaths around the world. It's a fairly standard shape for a bacterium – a sort of short, round-ended rod – and relatively immobile. Under the microscope, Yersinia pestis doesn't look particularly special.
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